1.3- Changes In Carbon Cycle Over Time

Question 1

Explain how the carbon cycle is in constant flux

Answer 1

• changes in carbon cycle have happened throughout history and continue to do so
• the scale of change varies through time and space
• some carbon may be stored in rocks for hundreds of thousands of years
• other carbon may cycle between stores very fast e.g. when wildfires break out
• these changes are often linked to altering temperatures in which global temperature has always fluctuated
• changes are happening at a range of scales through space and time

Question 2

Temperature changes affect the carbon cycle- explain the impact of cold conditions

Answer 2

• cold water holds more carbon dioxide, so is more acidic and therefore more weathering occurs
• colder temperatures affect the amount of forest cover and its location which affects the amount of carbon stored in biomass
• decomposition is slower in colder conditions so transfer is slower to the soil
• less water flows into oceans as more is frozen therefore less sediment is transferred to the ocean floor

Question 3

Explain the impact of hot conditions on the carbon cycle

Answer 3

• warm water holds less carbon dioxide
• warmer temperatures may lead to increased plant growth
• decomposition is faster in warmer conditions so transfer is faster the soil
• melting permafrost releases carbon dioxide and methane
• more wildfires may occur!

Question 4

We could divide the carbon cycle according to whether we’re looking at organic or non-organic carbon and whether we’re looking at long or short term cycling:

Answer 4

• fast organic carbon cycle= operates from months to centuries and includes transfers of carbon via living things between atmosphere, soil and biosphere
• fast non-organic carbon cycle= ocean-atmosphere exchange of carbon dioxide through diffusion
• slow organic carbon cycle= the long-term sequestration of in the remains of plants and animals over hundreds of million of years creating coal, natural gas and oil

Question 5

What are 3 other main physical causes of change within the carbon cycle?

Answer 5

• wildfires
• volcanic eruptions
• natural global warming

Question 6

Explain how wildfires can lead to changes in the carbon cycle

Answer 6

• wildfires can be started naturally by lightning strikes, however they are increasingly deliberately started by people i.e. arson
• wildfires can mean that a forest which should be a carbon sink becomes a carbon source ESPECIALLY when peat burns
• despite being restricted to minute parts of the Earth’s surface wild fires can have regional impacts
• in 1990s and again in 2013 there were many huge fires in Indonesia that burned out of control for months where smoke from these fires spread across parts of SE Asia affecting the lives of millions of people
• fires released vast amount of carbon dioxide into the atmosphere causing a noticeable spike in the rising trend of carbon emissions recorded since late 1950s

Question 7

Explain how volcanic activity can lead to change in the carbon cycle

Answer 7

• volcanic activity returns to the atmosphere, carbon that has been trapped for millions of years in rocks deep within the Earth’s crust
• at present volcanoes emit up to 380 million tonnes of carbon dioxide per year
• but by comparison, human activity emits about 30 billion tonnes of carbon dioxide per year, mainly as a result of fossil fuel combustion
• volcanoes also erupt lava which contains silicates which will slowly weather converting carbon dioxide in the air to carbonates in solution;in this way carbon is absorbed very, very slowly from the atmosphere

Question 8

What are human causes which lead to changes in the carbon cycle?

Answer 8

• combustion of fossil fuels

- land-use change: farming practices, deforestation and urbanisation

Question 9

According to the IPCC, about __% of anthropogenic carbon comes from the combustion of fossil fuels, primarily coal, but also oil and natural gas

Answer 9

90

Question 10

According to IPCC, about __% of anthropogenic carbon results from land-use change such as deforestation, land drainage and agricultural practices

Answer 10

10

Question 11

Roughly ____ of the anthropogenic carbon is absorbed equally by oceans and vegetation, and the remainder absorbed by the atmosphere

Answer 11

Half

Question 12

Since the _____, global concentrations of carbs dioxide have increased dramatically from about 320ppm to just over 400ppm, the highest level ever recorded

Answer 12

1960s

Question 13

Explain how combustion of fossil fuels leads to change in the carbon cycle

Answer 13

• fossil fuels are natural sources of energy formed from the remains of living organisms, primarily plants
• they are extremely important long-term carbon stores comprising carbon locked away within the remains of organic matter
• today, most of the world’s gas and oil is extracted from rocks that are 70-100 million years old
• the carbon has remained locked up in these deposits for all that time, but when burnt to generate energy and power, the stored carbon is released, primarily as carbon dioxide into the atmosphere, ACCELERATING THE RECYCLING OF THIS CARBON
• fossil fuels are mainly composed of hydrogen and carbon (hence term hydrocarbons)
• when combustion of methane for example occurs, reactions occur with oxygen releasing carbon dioxide and water

Question 14

Since the industrial revolution, fossil fuels have been burnt in increasing quantities, pumping carbon dioxide back into the atmosphere; once in the atmosphere, it enhances the

Answer 14

Natural greenhouse effect, increasing global temperatures- so called global warming. There’s been a dramatic increase since 1950, driven by the rapid industrialisation of developing nations such as China, as well as the continued demand for the world’s industrialised nations such as the USA

Question 15

Land-use change is responsible for about 10% of carbon released globally which impacts on

Answer 15

Relatively short-term stores and has direct links to issues of climate change and global warming. Furthermore, at the local scale, land-use change can have a very significant impact on small-scale carbon cycle

Question 16

Ploughing, harvesting, rearing livestock, using machinery filled by fossil fuels and fertilisers based on fossil fuels are all farming practices that release

Answer 16

Carbon

Question 17

On many farms, it is the use of what that is the main source of carbon emission?

Answer 17

Artificial fertilisers

Question 18

Methane is a potent greenhouse gas, and some farming practices result in high levels of methane emissions- explain how methane is produced from livestock, in particular, cattle

Answer 18

• livestock, especially cattle ruminate (regurgitate food) which produces methane as a by-product raising issues worldwide about the desirability of moving away from such a high dependence on meat and dairy
• cattle in the USA are estimated to emit around 5.5 million tonnes of methane per year into the atmosphere (around 20% of total methane emissions in the USA)

Question 19

Explain how methane is produced from cultivation of rice

Answer 19

• studies indicate that rice may contribute up to 20% of global methane production
• interestingly, research in Asia and North America has found that rice yields have increased by 25% due to increased levels of carbon dioxide in the air BUT this in turn has resulted in a 40% increase in methane emissions

Question 20

Rice is a primary food source for __% of world’s population, mostly developing countries so this trend is likely to continue

Answer 20

50

Question 21

Regarding deforestation, trees are removed either by

Answer 21

Burning or felling for building, ranching, mining or the growing of commercial crops such as oil palm and soya- the timber itself is also a valuable product in the production of furniture and other wood products

Question 22

Deforestation is widespread globally but is particularly concentrated in

Answer 22

Tropical regions e.g. in Indonesia

Question 23

In total, deforestation accounts for about __% of all global carbon dioxide emissions

Answer 23

20

Question 24

In a natural system, when a tree dies, it decomposes very slowly and releases carbon over a long period of time. During that time, new vegetation starts to grow that quickly compensates the carbon being released by the dead tree= system is carbon neutral. However, when deforestation by burning occurs

Answer 24

• carbon is immediately released into the atmosphere
• if the land is then used for a different purpose, such as grassland for cattle ranching, the future absorption of carbon dioxide will be reduced
• the system has now become a major carbon source rather than a sink
• this is extremely significant in terms of the carbon cycle both globally and regionally, as forest ecosystems are limited to certain regions of the world

Question 25

Replacing open countryside with concrete and tarmac is known as

Answer 25

Urbanisation

Question 26

Urbanisation is a major change in land-use that has a significant impact on the local carbon cycle- important stores are either

Answer 26

replaced (vegetation) or covered up (soils) with impermeable surfaces

Question 27

The major sources of carbon dioxide emissions from urbanisation include

Answer 27

• transport
• the development of industry, the conversion of land-use from natural to urban
• cement production from the building sector

Question 28

Cement is an extremely important material used in the construction across the world. Carbon dioxide is a by-product of a chemical conversion process used in the production of

Answer 28

Clinker, a component of cement, in which limestone is converted to lime- carbon dioxide is also emitted during cement production by the use of fossil-fuel combustion

Question 29

It has been estimated that cement production contributes about __% of global carbon emissions (although this is highly localised close to major cement-producing plants)

Answer 29

2.4